Digital devices such as, e.g., memories, shift registers, logical gates, and arithmetic units may be based on a variety of physical phenomena among which electrical and magnetic effects have been most widely exploited. One class of devices which has recently evolved to the point of commercial viability is based on the creation, propagation, and sensing of magnetic domains in a layer of a magnetic material. Early embodiments of such devices are disclosed, e.g., in U.S. Pat. Nos. 3,460,116 (issued Aug. 5, 1966 in the name of A. H. Bobeck) and 3,508,222 (issued Apr. 21, 1970 in the same name). Device disclosed in these patents are, respectively, a shift register and a memory readout device. Use is made in such devices of minimum-energy ferromagnetic domains, known in the art as magnetic bubbles, which are magnetized opposite to the general direction of magnetization of a layer of magnetic material.
A different class of devices, based on the use of ferroelectric materials, is in some respects similar to the class of magnetic bubble devices. However, the analogy between magnetic bubble devices and ferroelectric devices is incomplete and, in fact, no minimum-energy ferroelectric domains analogous to magnetic bubbles are known to exist. Ferroelectric devices are disclosed, e.g., in U.S. Pat. No. 3,142,045 (issued July 21, 1964 in the name of A. H. Bobeck) which discloses circuitry suitable for implementing a shift register. Various ferroelectric materials are disclosed in U.S. Pat. No. 3,936,146 (issued Feb. 3, 1976 in the name of A. Kumada et al) in the context of optical devices based on birefringence; similar devices are disclosed in U.S. Pat. No. 3,953,109 (issued Apr. 27, 1976 in the name of A. Kumada). Readout from ferroelectric devices is a concern of U.S. Pat. No. 3,701,122 (issued Oct. 24, 1972 in the name of J. E. Geusic et al) which discloses a shift register whose contents are read by an optical projection method.
Though established as to feasibility, digital devices based on ferroelectric materials have been developed to a lesser extent than those based on magnetic materials. In particular, development is incomplete, e.g., with regard to series coupling of devices and attendant need for energy gain by individual devices.